<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>显示年龄</title>
    <script>
        var age = prompt('请输入你的年龄: ');
        var str = '你今年已经' + age +'岁了';
        alert(str);
        
    </script>

</head>
<body>
    
</body>
</html>